The water soluble polyaniline of the present invention finds various applications as an corrosion protection of iron and mild steel in HCl medium and saline water.
There has been recently an increased interest in conducting polymer polyaniline (PANI), which has been studied extensively because of its unique proto-electron conduction mechanism. Epstein et al. in "Effect of Sulfonic Acid Group on Polyaniline Backbone", J. Am. Chem. Soc. 113 (1991) 2665-71 describes results on preperation and characterization of a self-doped conducting polymer (SPAN). J. Yue et al. in "Comparison of different synthetic routes for sulphonation of polyaniline", Polymer, 33 (1992) 4410-4418 has explained various routes and the effect of nature of oxidant, time duration and the effect of temperature on the formation of final product (SPAN). In this paper, characterization of all the products formed by different routes has also been studied although the starting precursor for all routes are same. N. Kuramoto et.al. in "Modification of Growth rate and structure of electropolymerized aniline by sodium polyvinyl sulphonate", J. Chem. Soc. Chem. Comm., (1990) 1478 have described the influence of polyvinyl sulphonate on the electropolymerization of aniline which modifies the electroactive and redox properties of the resultant film. In an another paper, J. Yue and A. J. Epstein in "Electronic control of pH at sulfonated polyaniline electrodes", J. Chem. Soc. Chem. Commu. (1992)1540 has studied the electrochemical modulation of self doped sulfonated polyaniline which can be used as a pH modulator. H. S. O. Chan et.al. in "Phosphonic doped emeraldine base", Macromolecules 27 (1994) 2159-64 explain better thermal stability without loss of a dopant species when polyaniline is doped with phosphonic acid esters. A recent paper by X. L. Wei ,Y. Z. Wang C. Bobeczko and A. J. Epstein on "Synthesis and Physical Properties of highly Sulphonated Polyaniline",J. Am. Chem. Soc. 118 (1996) 2545-2555) explains the details of synthesis and extensive characterization of LEB-SPAN. A paper by A. Talo et.al. "PANI/EPOXY coatings with good anticorrosion properties" Synth. Metals 85 (1-3) (1997) 1333-34 explains the complete electrochromical phenomenon of corrosion in presence of Hcl and also in presence of NaCl. A complete study of X-Ray Photoelectron spectroscopic study for corrosion protection of iron/steel by Emaraldene Base has been studied by M. Fahlman, S. Jasty, A. J. Epstein in "Corrosion Protection of Iron/Steel by EB PANI--an X-Ray Photoelectron Spectroscopy study", Synth. Metals 85 (1-3) (1997) 1323-26. Genies et al. in "Polyaniline--A Historical survey", Synthetic Metals, 36 (1990) 139-82 describes a detailed study on the electrochemical and chemical polymerization, redox mechanism and electrochemical properties of polyaniline. Another study related to corrosion is done by P. J. Kinlen et al "Corrosion protection using PANI coating formulation ", Pitture Vermici Eur 73 (17) (1997) 4847-53, in which PANI is used alongwith crylic resin primers and this also includes the whole study of salt fog tesdting done with PANI coatings. I V Yagova, S S Ivanov and V V Yagov in "Aniline based anodically polymerised coatings for corrosion--hydrogenation protection of steel," Prot. Met. 34(1) (1998) 51-53 have explained the effect of aniline polymerised coatings on the rate of corrosion A complete systematic study of PANI along with a series of epoxides has been reported by T. Page Mcandrew et al in "PANI in corrosion -resistant coating", ACS Symp. Ser. 689 (1998) 396-408. This paper also reports about good corrosion results of PANI especially when it is blended with other epoxides and diisocyanates. U.S. Pat. Nos. 5,164,465; 5,008,041; 789 095; WO 96 14, 343; WO 97 03, 127; WO 97 14, 729 had given detailed data of self protonated polyaniline, preparation of high molecular weight polyaniline and preparation of electrically conducting PANI salts having solubility in organic solvents and use of PANI coating formulations for corrosion protection. Reacting polyanilines with sultones can introduce an alkyl sulfonic acid group on the nitrogen atom of polyanilines (U.S. Pat. No. 5,641,859). Dehydrogenating polyanilines of emeraldine base with sodium hydroxide and then reacting with propane sultone, the reaction product, poly(aniline-co-sodium N-propane sulfonate aniline) exhibited relatively good water solubility, however since it is in undoped state, treatment with H-form ion exchange resin might be necessary to obtain green aqueous solution of poly(aniline-co-N-propanesulphonic acid aniline). Naguen and Diaz (macromolecules, 28 (1995) 3411 have synthesized copolymer of aniline and o-anthranlic acid which are soluble in alkaline aqueous solutions but they have a problem of low solubility in water. U.S. Pat. No. 5645890 (1997) provides an improved method of inhibiting the corrosion of metal substrate by applying a chemically deposited polyaniline on exposed surface of iron substrate SS-304 and SS-340. U.S. Pat. No. 589170 (April 1999) relates to a process for the water soluble self acid doped polyaniline which are prepared by reacting polyaniline derivatives with 2-sulphobenzoic anhydride in the presence of pyridine and N-methylpyrrolidinone and treating the reaction product with ion excahnge resin to convert into doped state. Japanese patents No. JP1092,220 (98 92,220); JP 0987,575 (97 87.515) and JP 06003813 (A2 94 0114)have given a description of water based electrically conductive PANI composites; manufacture of PANI based conductive polymer and technological uses of SPAN with its application to processibility.